Abstract Background & purpose: The benefits of adjuvant radiotherapy (ART) in gallbladder cancer (GBC) treatment remain inconclusive owing to the rarity of GBC and lack of randomized studies.Methods: PubMed, Medline, Embase, and Cochrane Library were systematically searched until March 2021. The primary endpoint was overall survival (OS). Comparative clinical studies that reported survival outcomes in GBC patients treated with or without ART were included. The comparability of each study was assessed by considering all possible clinical indicators (group 2: ART arm with poor clinical profile; group 1: ART arm with statistically similar profile or no evidence of having inferior clinical factors compared to non-ART arm).Results: Twenty-one studies involving 6876 GBC patients were reviewed. In pooled analyses of OS, the odds ratio (OR) was 1.26 ( p =0.111). In subgroup analyses considering comparability, the OR significantly favored the ART arm (1.92, p =0.008) among comparability group 1 studies, whereas it was 1.03 ( p =0.865) in comparability group 2 studies. The pooled rate of 5-yr OS in the ART vs. non-ART arms was 44.9% vs. 20.9% in group 1 and 34.1% vs. 40.0% in group 2. With ART, significant reduction in locoregional recurrence (OR: 0.21, p =0.001) but not in distant metastasis (OR: 1.32, p =0.332) was noted.Conclusion: ART not only showed benefits in patients with a similar clinical profile to those treated without ART but also yielded comparable survival in patients with an inferior clinical profile. Our results strongly support the more active application of ART in GBC treatment.Protocol registration: This study is registered in PROSPERO (CRD4202124062, available at: https://www.crd.york.ac.uk/).